This invention relates to a method and apparatus for atomizing a stream of molten metal into small particles in the preparation of metal powder and, more particularly, to such a method and apparatus in which an atomizing fluid impinges molten metal falling from a nozzle so as to form particulates therefrom.
It is broadly old to pass a stream of molten metal through a nozzle and to direct one or more high velocity fluid jets at the emerging stream to break up the sream into small globules which solidify into particulates of varying sizes.
However, nozzle arrangements for atomizing metal for use in making powdered products have left much to be desired. Some structures have proven to be undesirably sensitive to clogging because of the build up of solidified metal in the discharge passages or orifices. Another drawback of nozzle structures hitherto in use results from the contamination of the powder metal product by nonmetallics usually in the form of refractory particles abraded from refractory nozzles hitherto in use. Yet another common defect of such nozzles has been the production of too large a proportion of particles of sizes which require scrapping in order to avoid impairment of the density and uniformity of the product below an acceptable level.
The atomizing nozzle structure of U.S. Pat. No. 3,253,783 is illustrative of a structure susceptible to clogging and also abrasion of the refractory so as to contaminate the powder metal product. In that patent, the molten metal passageway 18 is relatively long and of small diameter so as to form an extended restriction in the path of the molten which has an undesirable tendency to clog in use. The atomizing gas nozzle is fitted to the pouring cup or tundish so that at least a portion of the gas stream impinges directly against the annular edge of the ceramic stem 16 through which the molten metal flows from the pouring cup, and this causes abrasion of the structure and contamination of the product.